This application is based on and claims priority under 35 U.S.C. Section 119 with respect to Japanese Patent Application No. 2000-373389 filed on Dec. 7, 2000, the entire content of which is incorporated herein by reference.
1. Field of Invention
The invention relates to a sheet feeder used in an image recording machine such as a printer, a facsimile machine, and a copier. More particularly, the invention pertains to a mechanism that separates a top sheet from sheets stacked on a hopper and feeds one sheet to a process station.
2. Description of Related Art
A known type of a sheet separator is disclosed in U.S. Pat. No. 5,895,040. This sheet separator includes a dam having a plurality of substantially parallel ribs extending from a base surface. One of the ribs is formed from a body of metal having a coating as its exterior surface, which has a low coefficient of friction over which sheets as recording medium move. The body has a longitudinal slot in its exterior surface. An insert, which has a high coefficient of friction with sheets, is supported within the body. The insert is preloaded so that a projection extends a predetermined distance through the slot for engagement with each advancing sheet. The high coefficient of friction of the insert initially engages the advancing edge of the sheet to cause the sheet to buckle or become corrugated. Then the portions of the sheet engage the low coefficient of friction of the exterior surface of the body to separate the sheet from the next adjacent sheet on the stack.
Another known type of a sheet separator is disclosed in U.S. Pat. No. 6,139,007. This sheet separator has slats disposed in the dam. One of the slats is formed with a plurality of protrusions or bumps arranged in a plurality of parallel rows, which are diagonal to the feed direction. According to this sheet separator, only one protrusion at a time engages the sheets to cause the sheets to momentarily buckle and then separate.
The invention provides an improved sheet feeder of simple structure having a stable sheet separating function and high durability.
Considering the foregoing, one exemplary aspect of the invention involves a sheet feeder including a hopper that holds a sheet in a stack; a sheet feed roller that touches the sheet on the hopper and feeds the sheet in a sheet feed direction; a face provided on a front end of the hopper with respect to the sheet feed direction so that a leading edge of the sheet being fed bumps into the face; and a plurality of protrusions that are disposed on the face and that bumps into the leading edge of the sheet when the sheet is fed, wherein the protrusions are placed on a plurality of lines parallel to the sheet feed direction, only one of the protrusions is placed on each one of the lines, and each one of the protrusions is separated from each other in a direction perpendicular to the sheet feed direction.
According to another exemplary aspect of the invention, the protrusions are arranged so that the leading edge of the sheet bumps into the protrusions at different points when the leading edge of the sheet is moved.
A point of the leading edge of the sheet, at which the sheet slides over a protrusion, does not bump into another protrusion at the downstream position.